Evaporative coolers have long been used to cool living spaces in regions of the world in which the ambient temperature is high and the ambient humidity is low. Some years ago, the use of evaporative coolers in the United States somewhat declined with the proliferation of full air conditioning refrigeration systems which are able to function effectively even when the humidity is higher than a level at which evaporative coolers are effective. However, in recent years, the remarkable increase in the cost of electrical power to the consumer has caused a resurgence in interest in and further development of evaporative coolers since evaporative coolers consume significantly less electrical energy than full air conditioning systems. It is not uncommon, for example, for homes and businesses across the southwestern United States to have dual cooling systems; i.e., both evaporative coolers and refrigeration. Evaporative coolers are employeed during periods of low humidity to effectively cool the designated space and also, as is well known in the art, to "air out" the space since the evaporative cooler draws in outside air and requires that the space be open to the outside (as through screened in windows and doors) to obtain the necessary circulation.
It is therefore understood by those skilled in the cooling art that evaporative cooling, given the necessary ambient condition of low humidity, is very cost effective in providing cooling for homes and businesses.
A typical evaporative cooler includes a blower motor, usually a two speed unit, which draws outside air through a pad or other element. The pad or other element may be wetted such that evaporation from the wetted element removes heat from the incoming air which is subsequently forced into the living space and thence circulates through the openings provided to the outdoors. The wetted element across which the incoming air is drawn is continuously wetted by a small pump which delivers water from a water sump. The water sump is maintained at an appropriate level by a float/valve hookup to a source of water, typically simply a normal cold water line. The blower motor may also be operated without the pump to simply draw outside air into the living space.
In the past, control systems for evaporative coolers have been rudimentary and, in some instances, dangerous. The most elementary control system is an on/off switch which controls the electrical power to the blower motor and water pump. Another such control system is referred to in the art as a "line voltage thermostat". This device is installed within the cooled structure and senses air temperature over a user-adjustable range of approximately 60 degrees F. to 90 degrees F. It responds by electrically switching one of the a-c power leads to the cooler's fan motor. These line voltage thermostats, while inexpensive, are inherently hazardous, unreliable, and cannot be Underwriters Laboratory listed. Most line voltage thermostats are designed and installed such that hazardous electrical voltages are present at or near the controls which are accessible to the user. Further, since most line voltage thermostats control the fan motor by switching one of the a-c power conductors, the device could be installed in series with the a-c common conductor. This type of installation contravenes the requirements of National Electrical Code, Article 380-2. Most dealers refuse to stock or sell line voltage thermostats because of their functional deficiencies and the potential of product liability claims.
Another prior art system employees a special evaporative cooler thermostat in conjunction with mechanical relay logic communicating on Class 2 wiring and voltages (i.e., low voltage, hence safer). This prior art system, however, has three distinct disadvantages: 1. it is expensive, 2. reliability is poor (mainly due to the use of mechanical relay logic), and 3. it is sufficiently complex to install as to be difficult for the ordinary handyman to achieve correct installation.
Thus, those skilled in the evaporative cooling arts will appreciate that it would be highly desirable to provide a cooler control system which is relatively inexpensive, very reliable, and very easy to install as well as being safe and approved by the appropriate testing laboratories and government agencies.